Lofting coordinates

"Fuselage station" redirects here. For fuselage-located weapon mounting point, seeWeapon station.

Lofting coordinatesare used for aircraft body measurements. The system derives from the one that was used in theshipbuildingloftingprocess, with longitudinal axis labeled as "stations" (usuallyfuselage stations,frame stations,FS), transverse axis as "buttocks lines" (orbutt lines,BL), and vertical axis as "waterlines"(WL). The lofting coordinate frame is similar, but not the same asaircraft principal axesused to describe the aircraft flight. For the US-manufactured aircraft the ticks on the axes are labeled ininches,(for example, WL 100 is 100 inches above the base waterline).

Two points on a fuselage at waterline 100/fuselage station 93 and waterline 101/fuselage station 276

Fuselage station

Fuselage stations on a scheme of a fuselage (atypically FS 0 is amidship, usually origin is at the nose, and FS values are nonnegative)

Fuselage stations are traditionally nonnegative, thus the origin is located at thenoseof the plane or, sometimes, ahead of it. When compared to the coordinates used foraeromechanics,the fuselage stations are measured in the opposite direction than the ticks on the x-axis (and might not be aligned at all, if the wind-aligned coordinate system is used to describe the flight).Some manufacturers use the designation "body stations", with the corresponding abbreviation BS.

Waterline

See also:Waterlines § Aircraft

Water lines on a scheme of a fuselage. Baseline is at the ground line, all WL values are nonnegative

Per theUS Air ForceAirframe Maintenance and Repair Manual (1960), a horizontal waterline extends from thenose coneof the aircraft to theexhaust cone.The base line of the aircraft is designated as waterline 0 (zero). The location of this base line varies on different types of aircraft. However. the planes of all waterlines above and below the zero waterline are parallel.The waterline number (WL or W.L.) in the US is expressed ininches,values increase upwards. Two typical alignments for the base line are the tip of the nose (negative WL are possible) or the "nominal ground plane" (measurements will be nonnegative).

Butt line

Butt lines on a scheme of astabilizer(BL ticks are symmetrical here, usually ticks on the left are negative)

Butt line ticks increase to the right of the pilot with the origin at thecenterline.When compared to the (right-handed) aeromechanics coordinate systems, the direction of the butt line is opposite to the y-axis.

Other

Other coordinate references on the aircraft body

Many other reference points are used, especially on a large aircraft:

• Aileronstation (AS), distance from the inboard edge of an aileron;
• Flapstation (KS), distance from the edge of the flap;
• Nacellestation (NS);
• Elevatorstation (ES);
• Verticalstabilizerstation (VSS).

Sources

• Takahashi, T. (2017).Aircraft Performance and Sizing, Volume I: Fundamentals of Aircraft Performance.Momentum Press.ISBN978-1-60650-684-4.Retrieved2024-07-02.
• United States. Air Force (1960).Air Force AFM.Department of the Air Force.Retrieved2024-07-02.
• FAA (2012).Aviation Maintenance Technician Handbook-Airframe.Aviation Supplies & Academics, Incorporated.ISBN978-1-56027-950-1.Retrieved2024-07-02.